1. Field of the Invention
The present invention relates to a process for the formation of vanadium phosphorodithioate compounds.
2. Description of the Prior Art
Vanadium dialkyl phosphorodithioate compounds have been described as effective catalysts in the preparation of copolymers of alpha olefins, e.g., ethylene/propylene rubber and ethylene/propylene/diene terpolymers. In U.S. Pat. No. 3,896,094 to H. D. Visser et al. such compounds are said to be manufactured by reaction between a vanadium halide or sulfate and a sodium or ammonium salt of a dialkylphosphorodithioic acid.
Reaction between the dialkylphosphorodithoic acid and vanadium halide to form vanadium dialkyl phosphorodithioate compounds in the absence of any substance to remove hydrogen halide by-product from the reaction medium is shown in C. Furlani et al., J. Chem. Soc. (A), 1970, 2929-2934. For example, on page 2929 of that reference vanadium (III) tris-O,O-di-n-propyl phosphorodithioate was indicated to have been prepared by reaction of vanadium trichloride with the corresponding acid. The resulting vanadium compound (or complex) was said to be stable for long periods under nitrogen but rapidly decomposed in air giving a black precipitate. Attempts to separate such a compound by extraction with organic solvents and then evaporation were unsuccessful.